CHAPTER XV. 
MUSSELS AND SNAILS. 
The Fresh-water Mussel (Anodon or Unio). These 
mussels may be easily obtained on the sandy bottoms 
of fresh-water ponds or streams. A few should be 
placed in an aquarium which has a few inches of sand 
on the bottom. They do well without feeding. Little- 
neck clams make good individual specimens for the 
work here outlined. Boil the clams to harden them. 
Notice the color and shape of the shell. How many 
parts has it ? 
Do you see any markings on the outside ? What do 
these seem to indicate ? 
Does the shell seem to be covered ? Compare it 
with a dried shell. Is the entire surface covered ? 
How do you explain your observation ? The bared 
projection is called the umbo. 
How are the two parts of the shell held together ? 
Is the hinge you find at the dorsal or ventral margin of 
the valves ? How can you tell ? 
In what direction does the animal move ? How fast ? 
Is the umbo nearer the anterior or the posterior 
end ? How can you tell ? 
Find the right and left valves. 
Observe the foot. How is it used ? 
Is it at the anterior or posterior end of the body ? 
At the end opposite the foot find the fringed open¬ 
ings. When the shell is open and the animal is feed¬ 
ing comfortably, color the water directly in front of 
these openings with a little indigo or cochineal solution 
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